The effects of plant density and weed competition on the growth, yield and yield. components of pigeon pea (cajanus cajan (l.) millsp.)

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Abstract

Two experiments were conducted at the National
Horticultural Research Station, Thika, Kenya, at an
altitude of 1550 m, latitude 1001'S and longitude
370 06'E. Tne experiments were .to determine the
influence of spacing on weeds, and on growth and
yield of pigeon~ea; and the critical'weed competition
period and effect of the length of this period on the
performance of this crop.
Two introduced short maturing and open
pollinated culti~ars of pigeonpea,
NPP 203/3 and NPP 291 were used in this study.
Eight weeding treatments were imposed on these
cultivars in the first experiment. In the second
experiment, however, only one cultivar, NPP 203/3,
was used with four weeding and 13 spacing treatments.
Results obtained in the first experiment showed
that weeding treatments did not affect the stand
count,plant heightJ date to 50 per cent flowering,
·number of seeds per pod and a hundred seed weight.
However, it was observed that the longer the weeds
were allowed to grow with the crop, grain yield, number
of primary branches and number of pods per :plant
decreased. It was also shown that the plots which
were kept weed-free throughout the season, upto
nine weeks and after.three weeks, did not differ
significantly (P <0.05) ~~grain yield.
These results suggest that the critical weed
competition period in the two cultivars is between
three and nine weeks. The twq cultivars differed
significantly in days to 50 per cent flowering, plant
height, number of primary branches, number of pods,
and grain yield, but not in stand count, number of
seeds per pod and a hundred seed weight. Soil
moisture was also slightly higher in plots where
weeds were not allowed to grow with the crop for a
longer period and that those plots planted with
cultivar N'PP 203/3 gave higher weed yields than
those planted with cultivar NPP 291.
In the second experiment, plant density did not
affect a hundred seed weight, number of seeds per
pod and plant height. Grain yield and shoot dry weight
per hectare, however, increased with increasing plant
density; whereas number of primary branches, number of
pods, grain yield, per plant, shoot dry weight per
plant and weight of dry,weeds per hectare decreased with
increasing plant density. It was also observed that
the longer the weeds were allowed to grow with the
crop, the lower was the grain yield, shoot dry
weight, number of primary branches, number of pods
(xiii)
per plant and soil moisture content. Plant height,
number of seeds per pod and a hundred seed weight
were not, however, affected by the various weeding
treatments.
An attempt has been made 'to discuss the results
given above and some conclusions drawn.